Semigroup approach to semilinear partial functional differential equations with infinite delay

We describe a semigroup of abstract semilinear functional differential equations with infinite delay by the use of the Crandall Liggett theorem. We suppose that the linear part is not necessarily densely defined but satisfies the resolvent estimates of the Hille-Yosida theorem.We clarify the properties of the phase space ensuring equivalence between the equation under investigation and the nonlinear semigroup.